Recently, with the use of the Internet and popularization of mobile telephones, content encryption to eliminate illegal copying of the content and use of recording media capable thereof have become common, and a system capable of reading and writing the encrypted content is being spread.
Conventionally, a mutual authentication is first performed between a content writing device and a recording medium when writing the encrypted content on the recording medium using the content writing device. In mutual authentication, a medium unique ID and a mutual authentication key saved in the recording medium, and a device key in the content writing device are used, and a medium unique key is generated. Then, a content key provided by the content writing device is encrypted with the generated medium unique key to generate an encrypted content key. The encrypted content key is stored in a protective area (area requiring authentication for access) of the recording medium. The content writing device further encrypts the content with the content key, generates an encrypted content, and stored the encrypted content in a data area (area not requiring authentication for access) of the recording medium.
In order to achieve stronger protection of the content between a recording medium and reproduction device, a recording method of recording the content on the recording medium using additional information provided from the outside of the recording medium is proposed (see patent document 1). When writing the content into the recording medium using additional information, a mutual authentication is first performed using a medium unique ID and a mutual authentication key of the recording medium, and a device key in the content recording device, and a medium unique key is generated. Furthermore, a composite key is generated from the medium unique key and the additional information. After encrypting the content key with the composite key, the encrypted content key is recorded in the protective area of the recording medium. Lastly, the content is encrypted with the content key, and the encrypted content is recorded in the data area of the recording medium.
With the wide spread use of systems capable of reading and writing the encrypted content, demands to distribute the encrypted content written on the recording medium in advance are increasing. When distributing a great amount of recording media storing the encrypted content, mass-copying of the recording medium having the same encrypted content is required, and thus a system capable of simultaneously writing the encrypted content on a plurality of recording media becomes necessary. A system for simultaneously writing data in parallel to a plurality of recording media is disclosed in patent document 2.
Patent document 1: JP-A-2004-139433
Patent document 2: JP-A-2000-259775